Small Form-factor Pluggable (SFP) modules are used in a wide range of telecommunication and data networking applications to interface between a printed circuit board in a piece of network equipment and a network cable (which may be electrical or fiberoptic). Typically, the SFP receptacle is mounted on the printed circuit board with appropriate electrical connections to the circuit traces on the board, and a connector at the end of the cable plugs into the receptacle. The connector itself commonly contains signal conversion circuitry and is therefore referred to as a “transceiver.”
QSFP (Quad Small Form-factor Pluggable) I/O connectors are commonly used for high-speed data interconnections. QSFP interconnects provide high port density and enable users to make better use of available linear printed circuit board (PCB) space. Some QSFP transceiver modules are provided with an integral cable, which is permanently connected to the module and may contain electrical conductors or optical fibers. In the latter case, the complete assembly of an optical cable with integral transceiver modules at both ends is referred to as an active optical cable.
Other sorts of QSFP modules do not have an integral cable, but rather contain a socket for a passive optical cable, i.e., a cable that contains only optical fibers without electronic components. For example, Cisco Systems Inc. (San Jose, Calif.) produces QSFP+ transceiver modules that are designed to connect to multiple-fiber push-on (MPO) connectors of a passive optical cable. MPO optical connectors are defined by the IEC-61754-7 standard of the International Electrotechnical Commission. The key component in these connectors is a ferrule having two holes for positioning pins and one or more rows of fiber holes, for accommodating a number of optical fibers, all with positions and sizes that are precisely defined by the standard.